# GGUF tensor reordering script with gguf-py plus hash verification > A duplicate tensor name raises ValueError. Parent: [Mac local LLMs: Memory and wired limits](https://llms-explorer.com/tree/mac-local-llms-memory-and-wired-limits/) · 1 facets · 15 facts · page: https://llms-explorer.com/tree/gguf-tensor-reordering-script-with-gguf-py-plus/ ## Facts - A duplicate tensor name raises ValueError. — source: `asserted` - Adding tensors after the file is opened raises ValueError. — source: `asserted` - Output is a new file; the writer does not edit in place. — source: `asserted` - With split_max_tensors or split_max_size set, tensors are partitioned into shards in insertion order. — source: `asserted` - Endianness mismatches cause a byteswap copy. — source: `asserted` - The exact posted script (Reddit r/LocalLLM 1vz927j) was refused by the fetch helper. — source: `asserted` - GGUFWriter keeps tensors as dicts and writes the data section in dict iteration order, with a code comment relying on Python dict insertion order. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - write_ti_data_to_file emits tensor info in the same order, with each offset equal to the running sum of ggml_pad(nbytes, data_alignment) of earlier tensors. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - The writer's default data alignment is GGUF_DEFAULT_ALIGNMENT and can be changed with an alignment setter, so a reorder must carry over any general.alignment value from the source. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - add_tensor_info raises ValueError("Duplicated tensor name ...") on a repeated name and raises if the output file is already open. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - add_tensor accepts raw_shape and raw_dtype for pre-quantized data, so existing quantized tensor bytes can be copied without requantizing. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - write_tensors_to_file raises ValueError if a tensor writes a different byte count than expected, so a short write cannot pass silently. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - With use_temp_file the writer spools tensors to a SpooledTemporaryFile (256 MiB in memory) and copies them at the end; without it each tensor is held until written, so a reorder of a 90 GB model needs the reader's memory-mapped tensor views, not copies. — [source](https://raw.githubusercontent.com/ggml-org/llama.cpp/master/gguf-py/gguf/gguf_writer.py) - Reorder recipe: open the source with GGUFReader, copy every KV pair, call add_tensor for each source tensor in the desired order with the large CPU-only table last, write header, KV, then tensors, then compare per-tensor sha256 and the tensor-info table (name, shape, type). — source: `asserted` - Name-keyed hashing (not offset-keyed) is the correct check because every offset changes after a reorder. — source: `asserted`